One of the reasons why diamonds are so popular as jewels consists in their inimitable brilliance. The brilliance peculiar to the diamond occurs in that a light going into a diamond causes internal reflections at its cut sides, and the reflecting lights are gathered at the table side (surface). Accordingly, the degree of the diamond brilliancy is largely influenced by cuttings and proportions of the diamond.
Diamonds of ideal brilliant cut pursuing brilliancy have proportions cutting off superfluous parts, and each of the cut faces look to the proper direction respectively. Thus, a major part of the light incident in the diamond regularly effects the internal reflections and is gathered on the table side, so that the greatest brilliancy is available.
On the other hand, diamonds which are roughly cut based only on carat (size) have proportions leaving extra excrescence and the cut surfaces face in random directions. Therefore the incident light cannot make regular internal reflections, and the amount of the light gathered on the table side is small and less brilliant. Further if the cut is very bad, some of the incident light passes through the rear side (pavilion) of the diamond without reflecting.
In shops, general purchasers normally observe diamonds with the naked eye, and the diamonds look almost the same in shining due to the illuminations or the like there, irrespective of good and bad cuts, and thus it is very difficult for purchasers without professionally trained eyes to distinguish between good cuts and bad ones.
Therefore, such the general trend is that are based more upon manufactures and sales attention to the carats which directly reflects on the prices than to the qualities of the cut and the proportions which are difficult to judge.
An instant observing instrument of the diamond brilliancy has been proposed in Japanese Utility Model Laid Open 60-109041, in which a diamond is placed between a magnifying glass and a light source, and a light from the source is applied to a red disc having a hole at its center and equipped to the side of an object lens of the magnifying glass so as to reflect the light against the diamond, whereby the diamond with much red light may be judged as having good brilliancy.
However, since said instrument needs a light source, it can be used only at places with electric sources, and is not handy. In addition, diamond patterns observed with this instrument are composed only of a white and a red of one kind (lighting parts are red and non lightening parts are white), and are particularly monotone. Light and shade of the patterns which are effected by strength and weakness of the light required to judge the diamond brilliancy, are not seen at all, and do not bring about steroscopic effect. The diamond brilliancy cannot be therefore judged fully and clearly.
The photographs used for professional opinions of diamonds and others are prepared by applying the illumination to the diamond from its downward direction and taking photographs with a camera from its upward side. The patterns photographed thereby appear such that the most brilliant parts and the least brilliant parts when viewed with the naked eye are blackish, and parts whitish. Such photographs are as follows:
1) Parts which should be seen most brilliant are taken black as if negative films of monochromes,
2) Since the most brilliant parts and the least brilliant parts are both taken black, it could not be discriminated which parts are really lighting, and
3) The parts to be taken white must include more brilliant and less brilliant parts than those inherently photographed ones, that is, strong and weak brightness, but the above stated photographs scarcely have light and shade variation caused by differences in brightness. So the brightness difference in the white parts cannot be distinguished at all.
Thus, the patterns do not produce a stereoscopic effect.
Non-professionals could not easily distinguish them, while the specialists could distinguish them somehow or other.
The present invention has been realized in view of these conventional problems, and the first object of this invention is to offer an instrument with which non-professionals can easily distinguish the good and bad brilliance of jewels as diamonds, and which is of a simple structure without requiring a light source, and is portable.
The second object of this invention is to offer a photographing method by means of the above mentioned instrument.